The present invention relates to a retractor (a wind-up apparatus) for a seat belt apparatus, and more particularly to a retractor for a seat belt having an energy absorption mechanism.
Hitherto, a retractor for a seat belt for safely supporting a passenger or the like in a vehicle seat has been an emergency locking type retractor having an emergency locking mechanism provided with an inertia sensitive means for reacting to rapid acceleration, collision or deceleration so as to physically lock the retractor in order to effectively and safely restrain the passenger, and arranged to moderate the pressure of the webbing to the passenger.
As an emergency locking type retractor of the foregoing type, a retractor for a seat belt disclosed in, for example, Japanese Patent Laid-Open No. 50-79024, Japanese Patent Publication No. 59-21624 and Japanese Utility-Model Publication No. 2-45088, has a structure having a locking means provided with an engagement member disposed at an end of a wind-up shaft, around which the webbing is wound, and arranged to be engaged to a receiving-side engagement portion of the retractor base in a vehicle emergency so as to inhibit the rotation of the wind-up shaft in a direction in which the webbing is drawn out.
The locking means has the receiving-side engagement portion, which is an engaging connection portion, provided for a through hole in the wind-up shaft for a retractor base through which the wind-up shaft is inserted or ratchet teeth formed in an internally-toothed plate provided for the through hole in the wind-up shaft. Moreover, a lock plate and an engagement claw, which are rotated together with the wind-up shaft, are employed as the engagement members. In an emergency of the vehicle, the engagement members and receiving-side engagement members are engaged to one another so as to prevent rotation of the wind-up shaft in the direction in which the webbing is drawn out.
Since a structure in which the rotation of the wind-up shaft is simply inhibited by a locking means wherein the webbing unintentionally gives the human body a shock attributable to a state of the emergency of the vehicle, a structure must be provided with which the webbing is drawn out if a load is further applied to the locking means after the rotation of the wind-up shaft has been inhibited. As a retractor for a seat belt of a type having the above-mentioned structure, an "energy absorbing apparatus particularly for a safety belt" disclosed in Japanese Patent Laid-Open No. 46-7710 has been known.
The above-mentioned apparatus has a structure provided with a wind-up member to which the force is transmitted from the energy absorbing apparatus and a holder structured to be relatively rotative with respect to the wind-up member. Moreover, a torsion bar (an energy absorbing mechanism) is disposed between the holder and the wind-up member. The torsion bar is twisted around the axis thereof so that the rotation of the wind-up shaft is inhibited by the locking means. When a load is further applied to the locking means, the webbing is arranged to be drawn out. In the above-mentioned structure, the amount of the torsion of the torsion bar is not limited.
However, the state where the amount of the torsion of the torsion bar is not limited raises a risk that the passenger sometimes encounters a so-called secondary collision in a vehicle of a type having a small space therein attributable to an excessively large amount of drawing of the webbing. Therefore, a countermeasure has been required to improve the safety.
Since shock, which arises attributable to a collision, is different owning to the structure of the vehicle, a load curve of energy absorption loads (loads which act on the webbing) must be changed to be adaptable to the characteristic of the vehicle to obtain an arbitrary load characteristic in order to satisfactorily protect the body of the passenger.
However, the energy absorption mechanism using the above-mentioned torsion bar involves the torsional deformation torque for the torsion bar being substantially constant. Therefore, the energy absorption torque is substantially constant in the overall operating range for the torsion bar.
An object of the present invention is to provide a retractor for a seat belt having a locking means and a shaft which can be twisted and exhibiting satisfactory safety.
Another object of the present invention is to reduce the size of a retractor for a seat belt of a type having a locking means and a shaft which can be twisted and exhibiting satisfactory safety.
Another object of the present invention is to provide a retractor for a seat belt which is capable of overcoming the above-mentioned problems and having a satisfactory energy absorption mechanism adaptable to the characteristic of the vehicle and capable of efficiently absorbing collision energy acting on the body of a passenger when the vehicle has encountered a collision.